So this only works if you're employer is flexible and lets you go home an hour early? It also seems like it would be in the employer's interest to prevent this

So this only works if you're employer is flexible and lets you go home an hour early? It also seems like it would be in the employer's interest to prevent this practice. You may be at your desk for an extra hour but you're eating lunch - work doesn't have your full attention. Overall you're probably working slightly less than the rest of the employees.